Temperature compensated switch



wg. 5, 1947. E. c. THOMSQN 2,42%64- TEMPERATURE COMPENSATED SWITCH medJan; 15,- 1944 i l ma u .if i

da O Patented Aug. 5, 1947v UNITED leirrlalv'lV OFFICE TEMErwrUar;coMPENsa'rEn lswrrcuy EllhuCraigThomaom Boston, Mass., assignor toCombustion. Control Corporation, Cambridge, Mass., acorportlonofiMassachusetts i 'Appueanqn January 13,y 19,44, serial No. 518,130

1 This-invention relates to electric switches and particularly toswitcheswhich are controlled or i tion by actuating elements depend forpositive and certain operationuponhdenite corelationof somma.(cileno-122) switch spring position and actuator deection, es-

pecially if one actuatcr is. supposed to yoperate several* contactsprings ,in` Va given sequence. While it is possible denitelytocorelatethe-switch operation to a given actuator deection, the latter ling thegenus of the invention. The description refers toa drawing in which e'Figs. 1 to 3 are elevations of a switch accordingto the invention, withthe actuator, contact,

and stop elements in various operative positions; Fig. 4 .is a detailview ofy a bimetallic switch spring according to the invention, and

" Fig. 5 a fragmentary elevation of a second em- I bodiment of theinvention.

Referring to Figs. 1 to 3, a suitable housing or frame, for example aU-shaped strip I (which may have aninsulating portion la), having tappedholes 2, 3 for mounting the switch on an itself may depend not onlyuponfthecoritrolling ef'lect purposely applied thereto butalso upon theambient temperature which, under' unfavorable conditions may even causevundesired. switch op eration without intended A,d'eiiectionpfl theactua-l tor.

plied thereto by a heating elementsince such actuators will respond tochanges' ofambient`temperature just as much as to the intendedtemperature changes of theheating element.

Itis one of the principal objects of the present invention tqprovide aswitch actuatedby a; device whose deiiection depends on its temperature,and the operation of whichhswitch is independentof ambienttemperatureconditions. Other Vobjects are to provide a switch ofthe typev`described inl Patent No. 2,358,372, dated September 19, 1944,l

which operates reliably, in. response ito, a; certain temperaturevchange applied by. a heating` element, regardless ofambienttem'peratureconditions; to providea thermally operated switchha'v ing two Iswitcnelements which .establish contact.

consecutively in predetermined sequence regardless of ambienttemperature conditions; antigen-v erally to provide. a switch o f Ithistype which Vis simple, rugged, inexpensive andyetvery accuraie.V

`These and v other objectsl yand `aspects will bel more fully apparentfrom4 thefollowingdescriptionjof several practical embodimentsillustrat- This undesirable veiiect is especially ,apt to occur when theactuator is puIDOsely designed to deflect in response vto temperaturechanges apt appropriate' support 4, holds between its arms by means ofscrew bolts 5, 6 a series of blocks I and a 'block 8 of insulatingmaterial. Betweeny these blocks and insulated from the bolts are clampedswitch spring strips I5, I6, II, IB constituting switch contactelements, and an actuating switch stripv I9. Screwed to end block 8 is a.bimetallic actuator strip 22 which can move only in a plane normal tothe plane in which strips I5 to I9 are operating,

Strips I9 and 22 are provided with heating resistors C and D,respectively. In normal, un-

heated condition, thesel thermal strips I9, 22 assume the positionsshown in Fig.v 1, Whereas when heated they bend as indicated in Figs. 2and 3. Suitable means may be .provided for adjusting the movement of thethermal strips I9 and 22.

Stops'25, 26 may be providedinf order t limit the movement of springsIl, I8 when they follow fiexure. of actuator I9 towards the right-handside of the iigures, assuring sudden breaking and closing of Contact atpoints CI and C2, with springs., I1, I8, ISat a definitelypredeterminable relative position.

The actuating contact strip I9, the contact springsll and I8 and stops25, 26 are made of bimetallic material for the purpose to be describedbelow.

Y Theiree ends of switch springs t1, I8 are bent over and downwardly ininverted U-shape With the more distant spring I'I reaching with lateralportion I'Ia over'the similar portion IBa of spring Iii-and thedescending portions E'Ib and I8b being arranged to contact spring I9 inunhcated position..

The switch springs I5 to I9 are provided with contactpoints constitutingswitches CI, C2 and D2; under-normal conditions, with bimetal strips I9and` ZZ-Kunheated, strip I9 retains contacts CI and C2 closed (Fig. 1)and insulating finger 24 of strip 22, constituting a stop element,closes switch D2,v The lower ends of the switch springs are extendedinto tails for connection with lead wires, as indicated at I I.

A resetting mechanism may consist of a cylindi'lcal block or bar 55 ofinsulating material which has two control faces or shoulders I, 52 andslides in two openings 53, 55 of frame I. Opening 53 is wide enongh to-permlt insertion of block 30, but screw' 55, if placed as indicated inFigs. 1 to 3. after insertion of the block 35 retains the latter in theframe without, however, hindering its sliding movement in openings 53,55. A spring 55 inserted between frame I and shoulder 51 of block Ilurges the block out of contact with springs I5, I5.

'I'he control faces 5 I, 52 are preferably so spaced that their distanceis greater than the distance of the stop faces of switch springs I5, I5in open position. Therefore, pushing in of block III by means ofresetting push button extension 55 will not close switch D, whereasrelease of the button will permit such closing, if the actuator 22 is inthe position indicated in Figs. 1 and 3; with element 22 in the positionof Fig. 2, switch D2 is open with spring I5 retaining actuator 22 indenected pition.

The heater coils C and D may be supplied with current through tailedlead strips 5I, 52, 53 and insulated connectors 54, 55.

Asmentioned before, and shown in Ilig. 1. all three switches CI, C2, D2are closed when the thermal strips I9, 22 are cold. When strip I9deflects, switchesCI and C2 are permitted to open, with switch CIopening ilrst as shown in Fig. 3, and switch C2 opening thereafter asshown in Fig. 2. If resistor D heats strip 22, the latter bendslaterally (forward in Figs. l to 3) and permits switch D2 to open aslikewise shown in Fig. 2. Flexure back into the position shown in Fig. lwill cause reclosing of switches CI and C2, the contacts being soarranged that switch C2 closes before switch CI.

The operation of switch elements 22, i5, I5 Iis explained in detail inthe above-mentioned patents and not described in detail herein sincethis aspect of the switch is not part of the present invention andmerely shown as belonging to the switch unit chosen for description byway of a well-tested embodiment of the invention.

Switches of the above-described type operate as follows.

When heater C does not carry current, actuator spring I9 contactssprings I1 and I5 and establlshes contact at CI and C2. Birnetallicsprings I1 and I5 are so mounted and dimensioned that, with changingtemperature, they deiiect in the same sense as actuator I9, so thatcontact at CI, C2, and the general mechanically effective relativelocation of the three elements is maintained regardless of prevailingambient temperature.

When current is for control purposes supplied to heater C, actuatorstrip I9 vbegins to bend ,away from strips I1 and I5 which follow theactuator, retaining CI and C2 closed, until strip I1 strikes stop 25whereupon C I opens as shown in Fig. 3. As actuator I9 deflectsfurther,A strip I5 strikes stop 25 and C2 also opens.

The eifectlve positions of bimetal stops 25 and 25 likewise change withtemperature so that, with proper arrangement which of course dependsupon the particular shape and dimension of every individual switchdesign, the mechanically effective position of contact springs such asI1 and I8, and stop elements such as 25 and 25 can be renderedindependent of ambient temperature.

When heater C is supply, actuator I5 deflects in opposite direction,first contacting spring I5 at C2 (Fig. 3) and then spring I1 at CI (Fig.1).

It should be noted that the construction shown in Figs. l to 3 isespecially advantageous to secure opening of one contact, as at CI,before that of another, as C2, for the following reason. Bimetal springI1 which is to open contact first at CI, is located furthest from heaterelement C,so that any possible heat transfer from C to I1 is less thanfrom C to Il.V Hence, deflection due to such transfer, of I1 and 25towards l5 is less than of I8 and 25 towards I5, which insures that thetendency of Ci to open first is enhanced rather than diminished, due tothe expedient of extending the contact point I1b effective for switchingat C I, over contact point 15b effective with regard to switch C2 thatdepends for operation upon the strip nearer to heater C and is requiredto open after switch CI.

The principle of the invention can be applied to different switchconstructions as for example that of the abve-identined patent shown inFig. 5. In this figure, I is the supporting frame, II1, II5 and Il!three bimetallic springs forming switch contacts vCI and C2, and 2l anon-conducting actuator strip carrying an insulating button 23 and aheater element C. The'strips H1, Ill, Il! and 2| are so arranged thattheydeilect in the samesense with varying temperature. so that theirmechanically elective relative position is not aliected by changes inambient temperature, in the manner described ebove. Deiiection of 2|towards the right of Fig. if),v upon heating by means of coil C, willcause opening of CI and C2, if desired in a predetermined sequence, "anddeflection of 2| in opposite direction will analoously cause closing ofCI and C2.

It will be understood that. although advantageously applicable toswitcheswith temperature sensitive elements actuated by any desirablemeans, the principle of the invention is especially advantageous if oneof these elements is purposely made temperaturey responsive and providedwith controlling heater means. as herein described.

It should be understood that the present disclosure is for the purposeof illustration only and that this invention includes all modificationsand equivalents which fall within the scope of the appended claims.

I claim: Y

l. A switch system comprising a switch base, an actuating elementadapted to deflect with changing temperature vmounted on said base,means for deflecting said actuating element. a switch spring elementtending to contact said actuating element, and a stop element limitinglsaid tendency of said switch spring. said switch spring and said stopelement being likewise adapted to deflect Iwith changing temperature,and said actuator element and said switch spring being so arranged andmounted on said base that flexure of said actuating element may causemechanical actuation oi' said switch element whereas temperature changesof actuating element, switch element and stop element leave themechanically effective relative location thereof substantiallyunaffected.

2. A switch system comprising a switch base, an actuating switch elementadapted to deflect with changing temperature mounted on said base, meansfor heating said switch element. a first switch spring element and asecond switch spring element likewise adapted to. denect with changingdisconnected from current temperature, said switch elements being soarranged and mounted on said base that flexure of said actuating switchelement through temperature change of said heating means may causecontact of said actuating switch element first with one of said switchspring element and thereafter with the other switch spring elementthrough mechanical contact therewith whereas temperature changes ofactuating and both switch spring elements leave the mechanicallyeffective relative location of the three elements substantiallyunafIected.

3. A switch system comprising a switch base, an actuating bimetallicswitch strip mounted on said base, a heating coil wound on said switchstrip, a first bimetallic switch spring strip and a second himetallioswitch spring strip, said strips being mounted on said base for coplanardeflection with said second spring strip arranged between said actuatingstrip and said rst spring strip, the ends of said spring strips formingcontacts extending towards the end of said actuating strip so thatflexure of said actuating strip through temperature changes of said coilmay cause disengagement of said end of said actuat- REFERENCES CITED Thefollowing references are of record in the Yille of this patent:

UNITED STATES PATENTS Number Name Date 2,035,426 Field Mar. 24, 19362,116,858 Winckler May 10, 1,938 2,274,399 Cook Feb. 24, 1942 2,358,372Wolfner 2nd Sept. 19, 1944 1,562,932 Walker Nov. 24, 1925 2,329,119Jacobs Sept. '7, 1943 2,129,477 Parks Sept. 6. 1938 1,783,904 Carter etal. Dec. 2, 1930

